A Swiss research team has been working on a way to identify the origin of pearls without destroying the valuable gemstones. Last week, they reported their success in extracting trace DNA samples from various cultured pearls in the journal PLoS ONE. Being able to capture the DNA fingerprint of a pearl will allow jewelers and traders to trace the origin and age of gems, and also pick out the fakes that are passed off as more valuable than they actually are.

“This DNA fingerprinting method could be used to document the source of historic pearls and will provide more transparency for traders and consumers within the pearl industry,” wrote lead author Joana B. Meyer, a researcher at the Swiss Federal Institute of Technology.

Despite what you might have heard, pearls are not typically formed when an oyster or mussel ingests a bit of sand. Pearls are actually more like shiny, pretty scabs resulting from an injury or parasite in a mollusk’s mantle tissue. In response to this injury, the shellfish creates a sac and deposits a mixture of the mineral aragonite and an organic compound called conchiolin, a composite typically known as nacre, also known as mother of pearl.

“Natural” pearls are produced in oysters without human intervention, and are considered far more valuable than “cultured” pearls. Cultured pearls are made by grafting a small piece of mantle tissue from one mollusk onto another, often also with a small hard bead that forms the nucleus of the growing pearl and ensures that the gem is as spherical as possible. Cultured pearls sometimes get passed off as natural pearls to unsuspecting consumers. Plus, some cultured pearls are made with haste, creating a flawed gem that’s mostly bead covered with a thin layer of nacre that chips off over time. The pearl industry would love to have a way to definitively determine a pearl’s origin.

But how do you squeeze DNA from a stone? The pearl, remember, is made from a mixture of inorganic minerals and organic material. And that organic matter, plus any stray bits of tissue that have ended up inside the pearl, houses DNA inside it.

In order to isolate DNA from the pearl without destroying it, the Swiss team used a very fine drill to expand existing holes in the gems. Using DNA scraped from the pearls, the researchers were able to trace sample pearls to three of the major pearl-producing oyster species: Pinctada margaritifera, P. maxima and P. radiata.

With this method, it may be possible to recover DNA from pearls that are centuries old. The researchers point out that other scientists have been able to extract DNA from ancient bones, teeth and eggshells.

The researchers anticipate that their methods, “coupled with detailed population genetic analyses of reference oyster populations could enable individual pearls to be assigned to specific oyster populations, allowing a scientific assignment of a pearl's origin.”

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